Interactive Use of Sign Language by Cross-Fostered Chimpanzees (Pan troglodytes )

Cross-fostered as infants in Reno, Nevada, chimpanzees ( Pan troglodytes ) Washoe, Moja, Tatu, and Dar freely converse in signs of American Sign Language with each other as well as with humans in Ellensburg, Washington. In this experiment, a human interlocutor waited for a chimpanzee to initiate conversations with her and then responded with 1 of 4 types of probes: general requests for more information, on-topic questions, off-topic questions, or negative statements. The responses of the chimpanzees to the probes depended on the type of probe and the particular signs in the probes. They reiterated, adjusted, and shifted the signs in their utterances in conversationally appropriate rejoinders. Their reactions to and interactions with a conversational partner resembled patterns of conversation found in similar studies of human children.